Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $221.46   6.356%   $235.536   $235.54   $235.55   $235.50  
  Purchase #2 $25.87   11.687%   $28.8934   $28.89   $28.90   $28.90  
  Purchase #3 $120.66   7.166%   $129.3065   $129.31   $129.30   $129.30  
  Purchase #4 $92.83   4.301%   $96.8226   $96.82   $96.80   $96.80  
  Purchase #5 $49.96   6.321%   $53.118   $53.12   $53.10   $53.10  
  Purchase #6 $62.49   8.325%   $67.6923   $67.69   $67.70   $67.70  
  Purchase #7 $165.36   11.189%   $183.8621   $183.86   $183.85   $183.90  
  7 purchase totals = $738.63       $795.2309   $795.23   $795.20   $795.20